The impact of foraging specializations and differential habitat use on the genetic differentiation of populations of two species of delphinid cetacean is being investigated. Killer whale (Orcinus orca) social groups (pods) pursue either marine mammal or fish prey, but rarely both. Variation at mitochondrial DNA and nuclear DNA loci among and between sympatric populations of each type of specialist forager are being investigated. There is little variation within populations, but significant differentiation between populations. Bottlenose dolphin (Tursiops truncatus) populations can be divided into "nearshore" vs "offshore" forms. The former pursue coastal fish species, while the latter prey primarily on cephalopods. Both morphological and genetic differentiation between these forms, and between geographic populations are found.